text:
Does the ground effect change with temperature changes?
The title is my question. Does the ground effect change as the temperature of the ground changes? In cold weather, a more cushion effect can be expected, and in hot weather vice versa?

No.  There is nothing in the physics of ground effect that depends on temperature.
On a hot day, you will have higher density altitude.  Your true approach speed will be greater (for the same equivalent airspeed).  You may perceive a difference in the way the landing feels because you are moving faster across the ground, but there is no difference in ground effect.
Also, on a hot day, thermals can form over dark areas of ground.  This convective activity can cause an aircraft on final to float.

I will assume:

You are asking about the temperature of the air near the ground, not the temperature of the ground itself.
The ground effect is the pressure caused by compression of air between the wing and the ground.
The ambient pressure does not depend on the temperature and the ground effect is isentropic.

The temperature of the air near the ground has a quite small relationship to the ground effect.  The ground effect can be simplistically described with the isentropic compressibility, which is inversely related to the square of the speed of sound.  As temperature increases, the speed of sound increases slightly.  This would cause an increase in ground effect.  The difference would be too small to be relevant to pilots or aircraft designers.
If you accounted for turbulence and phase changes (such as water condensing) then you may see other differences due to deviation from the ideal gas law.  These may be slightly less tiny near the melting point of water.

So much wrong here.  Ground effect has nothing to do with compressibility -- isentropic or otherwise.
Ground effect can be observed with potential flow assumptions (inviscid, incompressible).  Potential flow of an aircraft has boundary conditions that die off far away.  The ground plane inserts a plane of symmetry.  This can be replaced by placing a mirror of the flow across the symmetry plane.
So, if the wing was a horseshoe vortex, in ground effect, it would be the same as a mirror pair of horseshoe vortices in free air.
Temperature does not appear in potential flow.

Wind tunnels do have climate control. Many closed circuit wind tunnels include coolers to keep the flows' temperature from constantly rising during long runs.  Some wind tunnels are sealed and pressurized. This way, they run at higher than ambient pressure, helping them to match a desired flight Reynolds number. The NTF - National Transonic Facility at NASA Langley is a pressure tunnel that injects liquid Nitrogen to cool the flow (and keep it cold).  It does this to try to simultaneously match Reynolds and Mach number.

Some wind tunnel models are heated - and observed with an IR camera.  The differences in surface temperature can reveal where the flow transitions from laminar to turbulent.  These instruments are only sensitive for a narrow range of temperatures - this kind of experiment will only work with a tunnel operating over a certain range of temps.

Planes cannot fly in inviscid fluids.  2. Just because something can be observed under some assumptions does not mean the assumptions always apply when the thing is observed.  3.  You may be right about wind tunnels - I look forward to more answers to the other question.

https://physics.stackexchange.com/questions/111659/would-an-airplane-flying-through-superfluid-helium-experience-lift-and-drag

@RobMcDonald 4. Potential flow does not occur in aviation.

All models are wrong, some models are useful.  Potential flow is the_most_important theory for understanding aerodynamics.  The Euler and Navier Stokes equations may be more accurate in certain conditions (but still have simplifications and assumptions), and can be solved numerically -- but they provide almost zero insight and understanding.  All aircraft are designed and understood using ideas of potential theory. In this case, the inviscid assumption is presumably the one you're taking issue with -- it is irrelevant to the ground effect conversation.

Your link about superfluid helium is irrelevant.

"All aircraft are designed and understood using ideas of potential theory."  Designed, maybe, but the claim they are "understood" without accounting for compression is wildly implausible.  I took the question to be about reality, not models.  It would be best answered with a very precise experiment.  I have no further interest in your opinions about potential flow.

Compressibility is insignificant below about Mach 0.6.  Even high performance supersonic aircraft land at about Mach 0.3.  I.e. all aircraft takeoff and land in the incompressible regime.  Before you discount the importance of potential flow to understanding aerodynamics, I suggest you learn something about it.

@RobMcDonald In my opinion, the question is about tiny differences.  You have criticized without providing any equations or data.  Here is an experiment that shows the obvious fact air is compressible:  https://www.youtube.com/watch?v=TC6Me1zfyCM

I never said air was not compressible.  I stated how ground effect is studied, modeled, and understood by aerodynamicists.  I.e. By treating the ground as a symmetry plane and replacing the body with a mirror body -- and that this is normally done with potential flow models.  I have also stated that aircraft land (i.e. when ground effect is important) at speeds where compressibility effects are generally ignored.  You have made claims that potential flow is not relevant.  Open almost any book on aerodynamics, you will find the majority of it discusses potential flow.

@RobMcDonald It seems obvious to me that books would discuss potential flow - that tells us nothing about the question asked here.  Likewise, the practices of aerodynamicists tell us nothing about the question asked here.  Aerodynamicists should not care about tiny changes in the properties of air.  Appeals to authority are not going to change my mind about anything.  Try very precise data, or perhaps equations that account for very small effects.

Aerodynamicists would certainly care if it mattered.  They would certainly care about anything that had to do with ground effect.  Ground effect can be entirely explained without effects of temperature -- you have made no case otherwise.

@RobMcDonald "Ground effect can be entirely explained without effects of temperature -- you have made no case otherwise."  That is because ground effect can be explained without effects of temperature.  In my opinion the question is about something that doesn't matter for aviation.


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What happens to the pressure and density of air passing through shock waves?
I understand that the pressure and density of air increase as the air gets closer to shock waves and the pressure and density of air that has escaped the shock waves increase as well. Then, what happens to the pressure and density of air passing through the shock waves? I guess the density of air would decrease due to the great heat produced by the shock waves (correct me if I'm wrong on this) but what about the pressure? Does it increase because of the heat?

Please rethink your understanding of shocks.
In compression shocks, pressure and density increase suddenly without any change as the air gets closer or flows away from the shock front. All change happens momentarily as the air passes through the shock front. A compression shock is caused by an obstruction to the flow.
Supersonic speed means that the obstruction (a speeding bullet, or an airplane, for example) is moving faster than information about its presence will move through the surrounding air. This information would be a pressure change (like sound waves), but the propagation speed of such sound waves is determined by the physical properties of the medium through which they travel. Only exceptionally violent pressure changes can move faster than this limit - this is why you see first a rapidly expanding ball in movies of nuclear explosions which then abruptly changes to a much more leisurely speed of expansion as the ball grows and the magnitude of the pressure change at its boundary drops. (Note the spikes at the bottom of some of the fireballs in the linked movie: They are caused by the steel beams and tension ropes of the towers on which the bombs were placed. The speed of sound in steel is much higher than in air).

Still from high speed movie of a nuclear explosion (picture source)
The opposite of compression shocks are expansion fans: They let pressure and density drop over a region and are caused by a receding contour of said obstruction. Again, ahead and past the fan region the parameters do not change, but the fan region is protracted the more you move away from the contour change causing it.

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text:
What makes V1 one or two knots less than Vr on this performance table?
(B738 AFM, 0-2000 feet elevation, up to 27°C) Example of V1 and Vr differences.
The table shows that the V1 speeds are invariably one or two knots lower than their matching Vr speeds. Given that V1 can equal Vr, what's the limiting factor (probably factors) that puts V1 one or two knots below Vr? Vmbe might be one, but is it the only possible limiting factor here?
Or perhaps the V1 speeds are the same with the matching Vmcg speeds because that's operationally more advantageous in some ways than V1s being the same as the higher Vr speeds?
Or are the V1 speeds the speeds that bring the balanced field lengths, which require the mimimum runway distance?

It isn't a duplicate, but this is very closely related and explains how each of them are calculated: https://aviation.stackexchange.com/q/3564/69

V1 is the maximum speed at which you plan on rejecting takeoff should something go wrong, other than in situations where you have serious doubts about the aircraft's ability to fly e.g. catastrophic fire or structural failure before rotation. It is also tends to vary quite a bit depending on operational conditions. Aircraft manuals will have many tables, charts, and calculation instructions like the one above in order to allow pilots to calculate what their V-speeds will actually be on any given day... though, admittedly, this is usually handled by flight planning software there days.
Generally speaking, V1 is dictated by how much runway you require to stop and how much you have available to you. A lower takeoff weight or a lower density altitude will both serve to bring Vr down, which, ceteris paribus, can bring V1 and Vr closer to each other. A longer runway gives you more room to stop, so it can bring V1 up.
On a balanced field, V1=Vr so you have to option to reject the takeoff right until you're actually rotating. To look at it another way, you have as much time as you could possibly ask for in order to decide not to take off if you encounter a problem during the take-off roll.
As for Vmcg, this is the minimum speed at which you have sufficient control authority on the ground to overcome the adverse yaw you experience with the critical engine inoperative. It would only really come into play to make sure that you don't back yourself into a corner where, if you were to somehow have an engine failure, you also wouldn't have enough airspeed to be able to overcome the asymmetric thrust from the still-operating engine(s), so you wouldn't be able to continue to accelerate and take off safely, but are also going too fast to be able to stop within the available runway distance. Honestly can't say I could think of a situation where something like this could be an issue with anything but the most off-the-wall back country and bush flying these days.
FYI, in case I wasn't clear enough, an engine failure at or above V1 is not, by itself, grounds for rejecting takeoff. That's where your V2 number comes in. You rotate at Vr and climb out at V2.
The only time you would reject a takeoff above V1 is if you think that the chances of dying are greater if you get airborne than if you run off the end of the runway.

Thank you for your detailed explanation. "which, ceteris paribus, can bring V1 and Vr closer to each other." Could you clarify why this is the case?

Lower density alt. helps improve TO performance primarily in 2 ways: 1.) improved engine performance so your aircraft accelerates quicker and 2.) keeping you at a lower TAS throughout so the difference between the relative wind over your wings (and, by extension, the aerodynamic force available to you) and how quickly you're moving over the ground is adjusted in your favor. Stopping distance depends on how quickly you're moving. TO ground roll depends on how quickly you can get to Vr. Lower density altitude can help with both those aspects, though how much varies from one a/c to the other.

Lower weight simply means you can both take off at a lower airspeed and need less runway to stop. The interplay of how much this would help reduce V1 vs. Vr as weight decreases also varies from one aircraft to the other and, as your chart shows, may be more academic for certain take-off configurations (e.g. minimal flaps, as in your chart).

Wow, ceteris paribus. I had to look that one up.

@Terry: That's beancounter speak. Makes you even more likeable if you don't know that term.

Balanced field length numbers do not necessarily (or even usually) have V1=Vr....

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text:
Are ATCs required to notify pilots when they use MVAs?
I understand ATCs may use minimum vectoring altitudes(MVAs) when they deem it as appropriate. When they do that, do they notify the pilots of the fact that they are being radar vectored based on MVAs? Or are pilots expected to query ATCs when they find the newly assigned altitudes below the MEAs on the charts?

I'm not exactly sure what you are asking, but no, we do not notify pilots that we are vectoring in accordance with the minimum vectoring altitudes - because that is what we always do. ATC is responsible for terrain clearance during radar vectors, and pilots know this, so it is implied and understood that we use safe levels.
MVA's simply define the lower level for radar vectoring in an area - the lower level of our designated "box". Just like there is an upper limit and lateral limits as well, that we cannot cross during vectoring. MVA's are based on terrain and other obstacles, to ensure that terrrain clearance is always provided. You make it sound like MVA's are only used in special circumstances, which is not true. Vectoring at and above the MVA is completely routine and happens every day.
As for cross checking by pilots, MVA's are supposed to be published on a separate chart which pilots can use to cross check their assigned levels. The MEA is not used during approach, and pilots know this. In case of a radio failure during approach, if the flight is being vectored below minimum sector altitude (MSA), the pilot will climb to the MSA, even if the MVA is lower.
Further reading on SKYbrary.

If I want lower I will often ask ATC what their MVA is to see if it will work for me.

@J. Hougaard  I’ve never heard of MVAs being published on a chart for pilots and MVAs don’t show up on paper charts or ForeFlight. According to the Pilot Controller Glossary, "Charts depicting minimum vectoring altitudes are normally available only to the controllers and not to pilots." We’ve got lots of altitudes, MORAs, MRAs, MTAs, MSAs, but we don’t know the MVA.

@JScarry I don't know which country you are in, but it sounds like it is one that does not follow ICAO recommendations on the matter. The following three are examples from Sweden, Norway and Finland respectively: https://aro.lfv.se/Editorial/View/3112/ES_AD_2_ESGG_4-91_en https://ais.avinor.no/no/AIP/View/21/aip/ad/engm/EN_AD_2_ENGM_4-1_en.pdf https://ais.fi/ais/eaip/ad/efro/EF_AD_2_EFRO_ATCSMAC.pdf

@J.Hougaard Not surprising that the US doesn’t follow ICAO.

@JScarry, MVA charts are published by the FAA.  There is no assurance that the published charts are current, as radar, obstructions, etc. change the MVAs somewhat regularly.  There is little economic benefit to publishing MVA charts, so it is no surprise that ForeFlight doesn't republish them.

Sample MVA chart:  https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/mva_mia/pdf/D01_DEN_MVA_2013.pdf

@mongo Good to know. One reason they don’t show up on ForeFlight or in any paper charts is the caveat on the website,  "These charts are not geo-referenced and are not to be used for navigation. "


text:
Is flow turning different from the Magnus Effect? If so, how?

The production of lift is much more complex than a simple
  differential pressure between upper and lower airfoil surfaces. In
  fact, many lifting airfoils do not have an upper surface longer than
  the bottom, as in the case of symmetrical airfoils. These are seen in high-speed
  aircraft having symmetrical wings, or on symmetrical rotor
  blades for many helicopters whose upper and lower surfaces
  4-8
  are identical. In both examples, the only difference is the
  relationship of the airfoil with the oncoming airstream
  (angle). A paper airplane,
  which is simply a flat plate, has a bottom and top exactly the same
  shape and length. Yet, these airfoils do produce lift, and “flow
  turning” is partly (or fully) responsible for creating lift. As an airfoil moves through air, the airfoil is inclined against the airflow, producing a different flow caused by the airfoil’s relationship to the oncoming air (my emphasis).
PHAK pp.97-98

In what way is the "flow turning" being explained above different from the Magnus Effect (Bernoulli's Principle)? Are there any fundamental difference between the two? Aren't they the same in that they both use a speed difference in airflow between the upper and lower surface of an airfoil to produce lift?

The Magnus effect involves a spinning object, right? IIRC, Bernoulli's Principle will generally hold for subsonic airfoils and for the Magnus effect, but you need to know something about the lines of flow to apply Bernoulli. Why would you think these three things are not all different? What does Bernoulli mean to you?

OK, actually looking at the handbook, I see on page 96 it says that if you cut the teardrop in half and incline it, air flows faster over the top. No reason for the faster flow is given. Then it says the pressure difference alone does not account for lift (but how else can the reaction forces from downwash or flow turning be transfered to the aircraft?). And then a couple pages later it turns out you did not really have to cut the teardrop in half to achieve lift.

Dynamic lift is always created by "flow turning", or more precisely, by adding some vertical impulse to the oncoming flow.
There are several and equivalent ways to describe this:

If you draw a big box around the lift-creating object and integrate over its boundaries, the impulse change between incoming and outflowing air is equivalent to the lift being created inside the box.
If you look at the surface of the lift-creating object and integrate all local pressures over the surface, the result will be the same lift.
If you assume a bound vortex system inside the lift-creating object and adjust its strength such that you get the local flow speed around it just right, the circulation of the vortex system will create the same lift.

It is like with a boat, where buoyancy can both be described by the volume of water displaced by the boat or the static pressure acting over the wetted hull surface area. In all cases you get the same result, albeit in different ways.
In your case, "flow turning" is method 1 and Bernoulli is method 2. Both describe the same underlying process, albeit in different ways.


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The AFDS and A/T do not control to a speed which is less than minimum speed for the current flap configuration?

The AFDS and A/T do not control to a speed which is less than minimum speed for the current flap configuration. This speed is approximately 1.3Vs. Minimum speed, FMC speed, or selected speed, whichever is higher, becomes the AFS command speed. If actual speed becomes equal to or slightly less than the minimum speed the underspeed limiting symbol appears in the MCP IAS/Mach Display, and if operating in the V/S mode, the AFDS reverts to LVL CHG. The AFDS will also revert to LVL CHG from VNAV PTH, except when flying a level segment. [FCOM 4.20.36]

This paragraph is about the minimum speed reversion function of the 737 Automatic Flight system. Can anybody help me understand the first sentence? I don't understand what "control to a speed" means here. Does that mean the AFDS and A/T do not "respond" to the speed??

It means you cannot make Autopilot/Flight Director System and Autothrottle fly a target speed below your minimum speed for the configuration. If you were trying to set e.g. 50kts as your speed target, it would be ignored and replaced with the appropriate minimum speed.


text:
Why does the takeoff N1 limit start to decrease below 30°C OAT?

It's easy to understand why the takeoff N1 limit decreases with an increase in the OAT in the chart above; the engines get less dense air at higher temperatures, and less dense air means less engine power capability. But why does the takeoff N1 limit start to decrease with a decrease in the OAT below 30 degrees Celsius? For your information, the chart is an airport analysis chart for Boeing 737.

Not sure, so not giving an answer. But I expect another parameter becomes the limiting factor at cold temperatures, and the N1 maximum allowed must be reduced to avoid exceeding it.

I definitely don't find it easy to understand why the N1 limit decreases with an increase in the OAT. Because less dense air means a turn of the fan moves less air, but that also gives it less resistance, so it gives less power, but should be able to spin as fast.

Since this Q is in hot network questions: What are N1 and N2? for background for the idly curious wondering what this question is actually about.

What you see is called a flat rated engine. It means the maximum thrust from the engine is constant below the flat rated temperature (usually 30°C). Above that temperature, thrust will decrease due to the EGT (exhaust gas temperature) limit. In order to achieve a constant thrust at lower temperatures, the N1 needs to be decreased accordingly.

(CFM56-5A Lufthansa Training Manual, page 4)
See also:

What is a flat rated engine?
Why isn´t TOGA thrust always 100% N1 or N2?

There are basically 3 limits that the engine faces, temperature (maximum turbine entry temperature or maximum combustor exit temperature or sometimes maximum first stage HPT stator exit temperature), pressure (maximum compressor exit pressure) and stress (maximum stress in the blades and disks as a result of spool speed).
Varying the OAT for a specific engine design will hit one of these limits. When the OAT increases, the amount of fuel you can add to the system reduces as you get over-temperature, when the OAT decreases you could add more fuel, but that will increase spool speed which is also limited. From this figure you see the effects on SOT (turbine Stator Outlet Temperature, which is proportional to Turbine Inlet Temperature, TIT):

But why does the takeoff N1 limit start to decrease with a decrease in the OAT below 30 degrees Celsius?

The limit on the left is the decrease in spool speed, note that the corrected spool speed is constant (N / √(T)) so for a lower temperature, the N also decreases.

It's easy to understand why the takeoff N1 limit decreases with an increase in the OAT in the chart above

Yes it is, this is limited by the turbine inlet temperature (or a maximum exhaust compressor temperature as used in the image above, denoted as T3). The maximum turbine inlet temperature is fixed, the higher the inlet combustor temperature (exit high pressure compressor temperature), the less fuel can be added to heat to the air in the combustor, the less energy is available to expand in the turbines.
The constraining/limiting of the power output (thrust) is called flat rating.

This effect can be simulated with an engine model. If we would vary OAT for a certain power setting, e.g. constant (corrected) spool speed for a large bypass turbofan engine with imposed compressor exit pressure and turbine inlet temperature limit a model would look like:

After the variation of OAT you will yield the blue performance curves for a non-limited engine, and the brown dash-dotted curves for a limited engine:

Note that the compressor outlet pressure is the limiting factor in the graph on the left, but spool speed and compressor pressure are linked. The question is which of the two is reached first, this depends on the input and the design constraints.

Good Lord! An answer with a simulation!  Unreal.

What software is that? Is it free?

@ThomasWeller Yes it is free, but it is not appropriate at SE to promote your own software... If you look closely you see the product name and version number in the graph of the bottom image. Google is your friend.

Thanks, 0scar. IMHO it's ok as long as you disclose the affiliation. And to me it seems to be especially ok in comments after someone asked for it. Comments are transient anyway. For those interested: https://www.gspteam.com/products.html It has a free evaluation version.

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text:
What's the possibility of a commercial airplane crashing due to a computer error?
In line with this great question, what's the possibility of a commercial airplane crashing due to a computer error? Or are there already known cases of this? As a passenger, should you be worried about this possibility happening to you someday in the future?

"should you be worried about this possibility happening to you someday in the future?" Here is some advice: "Don't worry about the future. Or worry, but know that worrying is as effective as trying to solve an algebra equation by chewing bubble gum."

Air France Flight 296 had allegations of improper response by the computerized flight control system during the crash, but the official report stated pilot error. The computer did not allow more nose-up (alpha-protection engaged) to prevent going into a stall, however the captain said that it was an error in the fly-by-wire controls that did not give him elevator authority or increase the speed of the engines.

Do you really mean a computer error (e.g. the computer announces an error state, or produces incorrect output) or a general computer fault (something goes wrong with a computer system)?

First; let's be honest.  No one really knows what the exact probability is.
But we do have a design certification system that requires developers to apply various development assurance processes to meet specific safety standards for the design. The primary requirement is covered by §25.1309   Equipment, systems, and installations.
That has a lot of words about identifying potential faults and mitigating the associated hazards. But there are no numbers. As with most rules, the FAA conveniently provides an Advisory Circular to help you show compliance with the rule. In this case, its 25.1309-1A - System Design and Analysis.
The acceptable standard for critical faults (those with a potential catastrophic result) is found at the bottom of para 10.

(3) Extremely Improbable failure conditions are those having a
  probability on the order of 1 X 10^-9 or less.

So, if the developers do their job to the standard and the standard (and the methods used to evaluate it) are accurate the answer to the question is:
The probability is less than once in every 1 billion hours of operation.
As a point of statistics, that number applies to the cumulative hours of all aircraft of that design.

+1 for coming up with an actual quantitative regulation for that :)

What about periods of strong solar activity? VLSI chips are particularly sensitive.

@mins Avionics design must take into account the possibility of neutron single event upsets (NSEU) and include appropriate mitigation techniques. OEMs such as Boeing specify expected flux densities (the airframe does affect the value). Non-critical systems often just use watchdogs and reset if needed. Critical systems have more complex protections including ECC and mirrored memory and modified software to detect and correct errors due to NSEU. I've had circuits tested at Los Alamos Labs where they are bombarded with neutron beams. And to your point, it gets harder as the parts get smaller.


text:
Why don't single propeller planes rotate around the horizontal axis?
According to Newton 3rd law, every action has reaction force  in the opposite direction. That's how spaceship can move in space. That's why helicopter needs a second propeller in the back to prevent it from spinning in the opposite direction of the main propeller.
But why single propeller planes do not rotate around its horizontal axis opposing the rotation of its propeller ?

Actually, they do. Understanding Propeller Torque and P-Factor and Propeller Torque Effect

They do. That's why you apply opposite rudder to counteract the torque when starting the takeoff run.

I like how the dupe target is itself a dupe. :)

I remember seeing a doco about a Spitfire being restored. The last step for a conditional airworthiness certificate involved the inspector, upon returning from a short flight where roll trim was a problem (due to torque reaction) & the lack of cockpit aileron trim adjustment, taking two blocks of wood (while assuring that this was standard WW2 practice) & very carefully bashed a small part of the trailing edge of the aileron, slightly bending it a fraction of an inch over a few inches in length, so it would impart a force on the aileron at cruising speed to counter the roll tendency. It worked

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text:
How much power and lift margin do helicopters have for hover?
Suppose you are designing a helicopter and trying to size the rotor system for hover and flight. Your helicopter has a certain gross weight at sea level, standard atmosphere. How much additional lift margin do you design into the lift system? Or worded another way, how much margin do you add to a flight envelope?
Since there is ample information on the Robinson R44, let's consider:
Wikipedia says:
Gross Weight: 2500 lbs (1134 kg)
Rotor Diameter: 10m
Powerplant: 245 hp (183 kW)
In theory this is at Sea Level, Standard Atmosphere.
But would there be additional rotor lift margin for the helicopter's rotor to be able to maneuver, and for safety? For example, I imagine the R44 would actually be capable of lifting 3000 lbs (suppose) at sea level, and with the 183kW, but this is derated to 2500 lbs for operational safety. I'm not talking about the structural safety margins for the components, for which the FARs are pretty clear in general, I'm after the aerodynamic forces here.
Given my experience flying, I don't expect it to be much, but curious to see if there is any reference/standard/custom. Thanks!

Key here is density altitude, and weight.  There will be charts and graphs in the POH for this.

Civil helicopter certification requires stall-free operations at 1.15g and mtow. This should be the value you're looking for. Anyway the design of the main rotor is much more complicated than that and fundamentally dependent on the customer requirements and/or intended use.

Let me know if my comment answers your question, if so I'll convert it into a proper answer

Hi sophit, yes that was the answer I was looking for!


text:
Do Medevac aircraft need to maneuver within stricter attitude limits to ensure the safety of the patient?
Do Medevac aircraft need to maneuver within stricter maneuvering/ attitude limits to ensure the safety of the patient?
Or are there recommended operating practices?
Ie:

Are there pitch limits that would negatively affect the patient?
Do Medevac aircraft need to fly with reduced bank angles?
What about yaw?
I presume that slipping would not be advised, but may be necessary?
G loads would have to be positive as much as possible, though this may not possible in rough weather/turbulence?

Related: Does the FAA have specific Air Ambulance safety guidelines? Air ambulance is the term used by ICAO/FAA and several other agencies, as well as EMS (emergency medical service), medevac being initially a military operation.

If you're sick enough to need an air ambulance, you're not going to be up and walking around, and certainly not getting a drink from the first-class bar. On the other hand, the flight nurses may have to, so they're the ones to get injured.

That would depend on the nature of the emergency and the health of the patient.
For example I know someone with severely reduced lung function, she can't fly at normal cruise altitudes for commercial aircraft because the cabin air would be too thin for her to survive, so when she flies (medevac only these days, obviously, or light aircraft or helicopters) the aircraft must stay below 10.000ft. For someone being evacuated with just a broken leg that'd not be relevant (most evacuation flights here are of that nature, returning people with injuries related to ski accidents home for recuperation).
Medevac flights, like all commercial flights, tend to avoid violent maneouvers anyway, for comfort and to reduce structural stress on the aircraft. They also try to avoid inclement weather for the same reasons (normal aviation safety). All of that covers pretty much everything in your list already for any commercially operated aircraft, not just medical flights.
Obviously for military evacuation flights out of combat zones all that goes out the window at least until you're out of reach of enemy ground fire, and to a degree that might also be the case if the medevac helicopter or aircraft has to land in unusual spaces where some unusual maneouvers would be needed to get in and out of there (this might even affect some hospital helipads, not all hospitals were built with them in mind and retrofitting them sometimes left them in tricky spots).

And not everything can be done at ideal case. Weather, airport location, etc. may require not ideal setups. In any case most of them is briefed before the mission (or also during it) -- also note: "patient" may be just an organ, so speed is more important compared to "comfort")

@GiacomoCatenazzi of course, and in that case (and in case of entire human beings) the person or item being transported will be appropriately packaged (padding, restraints, maybe an oxygen mask, maybe even sedated).


text:
Is there any way I can check the status of my medical?
I was deferred my third class medical because of a certain condition and the doctor said I’ll hear from the FAA in about 3-4 weeks with either my certificate  or they’ll ask for more information.  It’s been 3 weeks going on 4th week, and I’ve heard of them taking 2 months or longer so I was just wondering is there any way I could check the status of my medical like it can tell me it’s been sent back or is currently being reviewed or etc?

On the off chance that anyone is thinking of closing this: This is not a duplicate of https://aviation.stackexchange.com/questions/15176/is-there-truly-no-way-to-get-information-about-medical-application-status, because nowhere on that page does anyone say how to check the status of your medical application (and that information would not be appropriate as an answer to that question).

The standard way to check the status of your medical application is to call the Aerospace Medical Certification Division at (405) 954-4821.
When you call, it's very likely that you will hear a recorded message saying that due to high call volumes, they are unable to assist you. If you do, call again later. When I was checking on the status of my own application, I had to call quite a few times before my call was finally answered.


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Is this a type of navigation aid?

I saw this contraption on the southeast corner of Eastern West Virginia Regional Airport, Martinsburg, WV (MRB). My first thought was this was some kind of NDB antenna but not sure.

Can you pinpoint it better? I don't see it here https://www.google.com/maps/place/Martinsburg,+WV/@39.4060262,-77.9711287,715m/data=!3m1!1e3!4m5!3m4!1s0x89ca0269b6b66563:0x96b0844a782376c7!8m2!3d39.4562099!4d-77.9638869

Air National Guard Base, might be something they use.

It’s located to the east of the cafe on the south side of the main runway on google maps.

Ok, I see it. Not airport related for navigation. No idea what it is. Not indicated on any approach chart, or the airport diagram.  https://aeronav.faa.gov/d-tpp/1908/00249AD.PDF

This could be an abandoned NDB.

If you go to www.skyvector.com and zoom in to MRB
(easy to enter a flight from KOKV to KMRB to find it quick)
Select the World VFR view, and you will see no navaids at that location.
Select the Enroute L-29 view, and you will see no navaids at that location.
So no, it is not a type of currently used navigation aid.
If you peruse the Instrument approaches for KMRB at Airnav.com  https://www.airnav.com/airport/KMRB
you will also not see that structure mentioned.
Airport phone numbers are listed, you could call up and ask what it is.

Main thing is, it seems to be a receiving antenna, not a transmitting one.

if it's an antenna at all. Could be part of a weather station for example. Seems to be some vehicle traffic over the grass towards it, so it is in active use and requires people to access it physically with some regularity.

@jwenting - hard to say if the tower itself is actually serviced regularly, as such tracks could easily be from people going in and out of the gate just to cut the grass inside. [Which itself could be more related to wildlife abatement than anything to do with the structure. working around old stuff is often easier/cheaper than bothering to rip it out.]


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Why do some AFBs have planes parked at 45 degrees to others?

I'm assuming this is just a matter of available space but it seems you could get 4 across all aligned but maybe there is another reason. The image is from McGuire AFB but I've seen this on other AFBs.

I see it at Beale AFB, Tinker AFB, March AFB and Albuquerque Airport. There seems to be a lot of various layouts for fighters and tankers/cargo. Some are all aligned while some are all at 45s, but there are a few mixed and I'm just not sure why.

Because that's how the lines are drawn on the ground.

To protect them from Japanese saboteurs.

Look at the spacing of the planes.  The angled ones are closer to their neighbors.  But if you did them all that way you wouldn't be able to get them as close.


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Why are there no high wing Canard airplanes?
Just had a thought about canard airplanes while looking at the Tu-144 that features a canard surface on the top of its fuselage.
Are there any high-wing aircraft with a top or bottom mounted canard? What are the deficiencies that make the configuration so uncommon?

I believe that at least some aircraft on this list would qualify as "high-wing"

E.g. all the MacCready "Gossamer xxxxx" aircraft

Almost all Rutan-designed (or derived)aircraft (Long EZ, Varieze, Berkut, etc.) are high-wing... (except for the canopy anyway)

Might better ask "why are there so few high wing aircraft" in general.  All the same considerations apply.

@ZeissIkon I'm not sure if you meant that literally, but per Wikipedia 4 out of the 5 most-produced civilian aircraft of all time are/were high-wing: C172, C182, C150/2, J-3.

If we wanted to split hairs, we could point out that the early Wright gliders and airplanes had canards and a high wing (and also happened to have a low wing too...)  -- likewise Curtis June Bug, Santos-Dumont 14-bis, etc   : )

@Pondlife On the other hand, outside the fairly narrow civil light plane market, the vast majority of all types are low, mid, or shoulder wing for reasons of gear height/weight, visibility, and structural weight.

https://disciplesofflight.com/king-katmai/
There’s at least one.

Who says there aren't?
MiG Utka (source): High wing, low canard. Sources say it was a pleasure to fly.

Focke-Wulf 19 Ente (Ente means the same in German what Utka means in Russian): High wing, high canard. It was built to research canard configurations.

A high canard is unusual when ahead of the cockpit because it restricts the pilot's field of view too much.
For the drawbacks of canards in general please see this answer or this answer. If you ask yourself why you always read how much better canards are, consult this answer.

A high canard not ahead of the cockpit... Saab Gripen and Viggen are all I can think of.

I remember all the fanfare when Rutan introduced the Vari-Eze, and his "secret" to fixing the pitch behaviour issues inherent to canards, with the U of Glasgow airfoil. Then it turned out the airfoil couldn't tolerate any contamination, even rain, so people put VGs on the canards, and finally John Roncz came up with a modified canard airfoil that didn't need the VGs.  In any case, main selling point for the airplane wasn't so much that it was faster than a normal configuration, but that you got high speeds from high wing loadings without the stall risks.

A pleasure to fly perhaps, but not to behold, dear god almighty what an ugly duckling...

@CamilleGoudeseune Eurofighter also - all three really more mid-wing canards with low-wing deltas.

"Ente means the same in German what Utka means in Russian" – And just to be clear: the German word "Ente" and the Russian word "Utka" mean the same as the English word "duck", which means the same as the French word … "canard".

@CamilleGoudeseune What about the XB-70? Also a high canard, but a low wing.

@JörgWMittag I thought this was obvious. Canard and Ente even have the same double meaning.

@PeterKämpf Only obvious if you speak both French and German...

@PeterKämpf which double meaning?

@htmlcoderexe A canard is a falsehood, mostly when printed in a newspaper. This is even used in English, with the French word. Only Wikipedia doesn't know this.

@PeterKämpf thank you for your insightful answer!

@PeterKämpf huh, that's maybe where Russian got it too as it also has that exact extra meaning - basically like a newspaper hoax

@htmlcoderexe You're right, and they have translated the "canard" into gasjetna utka (newspaper duck).

I've never seen the Ente before.  I would have guess that its construction was some kind of industrial prank.

@acpilot As a research airplane, it was one of a kind. And it cured everyone involved from following up on it.

Are there any high-wing aircraft with a top or bottom mounted canard?

No one could deny that the Aviafiber CANARD 2 FL was a (very!) high-winged aircraft with a forward-mounted canard.  The wing was mounted very high above the fuselage on long diagonal struts, while the canard was at the level of the fuselage.  For photos, visit http://www.delta-club-82.com/bible/photo.php?id_aile=568&langue=en

There was also a motorised version of it.
More info--
https://www.delta-club-82.com/bible/568-hang-glider-canard-2fl.htm
https://en.wikipedia.org/wiki/Aviafiber_Canard_2FL

See also the Gossamer Condor and Gossamer Albatross human-powered aircraft.

Perhaps some of these also qualify--
Duck hang glider
Gyrfalcon hang glider
Mk 2 Splitwing Circa hang glider
And this unknown hang glider

But the real "nuts-and-bolts" answer to your question is this-- considering aircraft with a conventional enclosed cockpit or "cabin"-- if the aircraft has a horizontal stabilizer in the rear and an engine in the front, then one of the logical places to put the wing, as far as the fore-and-aft trim and stability is concerned, is on top of the cockpit or cabin.  (Putting the wing beneath the cockpit or cabin can also work out well.)  Once you move the engine to the rear and get rid of the rear horizontal stabilizer and add a (lifting) canard, it tends to work out best to put the cockpit or cabin in front of the wing, as far as the fore-and-aft trim and stability is concerned.  This tends to rule out the option of putting the wing on top of the cockpit or cabin.  (Or perhaps it would be more accurate to note that this tends to allow the designer the option of putting the wing more or less on the same level as the cockpit or cabin, without having structural parts run through the cockpit or cabin space.)  But as other answers have shown, there are exceptions to every rule or generalization--even in such a case, there are still ways to mount the wing above the level of the cockpit or cabin, so a few such designs do exist.

Reading your answer, I remembered that I had a photo of the Aviafiber Canard  in a motorised version. During the flyby it fluttered like hell but the pilot was undeterred and kept the speed up.

@PeterKämpf -- nice addition, thanks

@quiet flyer Thank you for sharing those obscure designs! Very interesting!


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How do electric propeller governors (or electrically controlled governors) work and what are their pros and cons?
I am trying to understand why electric propeller governors are not (yet) prevalent given that they offer the ability to control the RPM with high accuracy. What is the typical architecture for an electric governor or electronically controlled governor? What are their pros and con?
As far as I know, there are two types of electric governors:

The governor has an electric actuator in the propeller hub like the Airmaster Governor. This removes a lever, but adds a number of switches in the cabin.

The governor is still hydraulic, but an electric actuator controls its position. (I think the PC-12 and TBM700 work like this?)

I am assuming that option 2 is not ideal as you need a separate actuator to control the governor cable.
I guess I do not understand how airplanes like a PC-12 or TBM700 (that only have a single lever in the cabin) regulate propeller RPM.
Thanks!

The presence of manual control is rather orthogonal to the mechanism used for governor and actuator, just like you can have autopilot with mechanical or hydraulic controls. Are you asking about how the automatic RPM control (of e.g. PC-12) works (which still allows different kinds of actuation) or how the electric governor + actuator work (which still may be controlled manually or automatically)?

In short, I wanted to know both! It basically seems to me like the number of functions the governor/actuator mechanism needs to perform are too high for a single lever to control everything. Edit: I have seen diagrams for the PC-12's hydraulic governor that keeps RPM constant. It does not allow for varying RPMs however.

They are much more prevalent than you think, and have been in use for more than 70 years. Rotax 912 and 914 engines can be installed with electric governors from MT Propeller. Airmaster sells them as well. You may also be surprised to learn that nearly 90% of German operational Luftwaffe aircraft during WW2 used an electrically-actuated propeller system designed by Dr. Hans Ebert of the VDM (Vereinigte Deutsche Metallwerke, or United German Metalworks). One example of these excellent propeller systems is in the Smithsonian's National Air and Space Museum.
This article does a pretty good job of explaining how they work.

The WW2 VDM units were not even constant-speed though, were they? My understanding is that they were just electrically actuated, but the pilot set pitch, not RPM, so they had no governor (governor is the part that senses RPM for the constant-speed feedback loop). Or did they?

I didn't say the German props had a governor. Also, many of the electrically actuated props on modern aircraft are not governors either. You just select the pitch you want, often from a fixed number of options.

Indeed, but the question asks about governors, so it would deserve to be stated explicitly.

Thanks for sharing the MT Propeller link and the WW2 era technology. I also found pictures of the MT Propeller's control box on the instrument panel, and it looks similar to Airmaster's: https://backcountrypilot.org/forum/mt-electric-adjustable-prop-12019

Electric stephead motors (governor motors) have been around since prior to the second world war.  I used to run them on various old radials such as R-2600's.  These accomplished the same thing a manual control would do, in changing tension on the speeder spring in the prop governor.  Instead of moving a lever in the cockpit, one moved an electric switch in the cockpit.
In the case of the old radials, setting RPM using a stephead motor assembly was more about finesse; the change dind't occur immediately or in a liner relation to holding the switch fo ra given period of time.  One could hold the switch and see no immediate change, and assume it required being held longer.  Then one ended up holding it too long, and the RPM rolled back too far.  Setting RPM on takeoff, or fine tuning it, was purely a matter of experience (trial and error).
Most constant speed propellers, from the hamilton standard hydromatic three quarters of a century ago, to most propellers today, use the same basic function of using a pilot valve to admit oil to the propeller mechanism, and that oil, under pressure, drives prop blades to the angle necessary to maintain a specific RPM.  The pilot valve is controlled by a spinning flyweight, and the flyweight travel and action is controlled by spring tension against the pilot valve.  The electric motor controls the spring tension.
Various engine installations also use feedback from other engine components, such as power lever, and governing comes from several sources; RPM may be held constant, and engine power is regulated using fuel governors, overspeed governors, underspeed governors, and fuel topping governors.

Interesting! I did not know that the old radials had electric stephead motors to adjust propeller pitch! I will look into the R-2600s. I only have some exposure to the R985 with the hydromatic. It is amazing to see the many ways to optimize the propeller to the engine/motors.


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How does a Delta-3 hinge on a helicopter tail rotor work?
I am trying to understand how adding offset hinges would provide a self-feathering force.  Does anyone have more information on Delta hinges on helicopters? I am a bit confused with the information I have available. A video would be nice, but I couldn't fidn much on YouTube.
Here are two references illustrating the concept, and a picture from the first link (b).
Delta-3 Hinge
Delta-3 Hinge - AOPA Explanation

The AOPA explanation does not have the offset/angled blade:

It's because the blade's span-wise axis is "swept" relative to its flapping hinge line, so when it flaps, the sweep angle results in the blade's effective AOA changing somewhat (for the advancing blade, reducing; that's what the feathering part means).
To picture it, imaging you are standing directly in front of the tail rotor disc watching the advancing blade of the plain rotor come over the top or bottom straight toward you.  All you see is its thin leading edge.  If the plain blade flaps left or right, still all you see is the thin leading edge because the blade's axis is perpendicular to the feathering hinge axis.
Now imagine the Delta three rotor blade from the same vantage point, and the hinge flaps left or right. Because the blade's span-wise axis is offset, or  "trailing" the flapping hinge axis, you will be able to see some of the upper or lower surface of the blade from your vantage point when it flaps. To the airstream, this is effectively a slight reduction in AOA ("feathering") compared to the AOA of the unflapped blade as set by the pitch change linkage (or an increase when flapping while retreating).

I think that makes sense! Thank you!

There's a tiny flaw in the explanation.  There exist both negative and positive delay 3 hinges   Notably on Bell helicopters the blade "in" feathers with flapping.  See my explanation below

Delta-3 (also spelled $\delta_3$) is a simple yet difficult to visualise concept.
I suppose that the best way to understand it is by comparing a rotor with a built-in delta-3 with one without it. The following two rotor heads are both taken from Wikipedia (plus a couple of colorful lines from my side): the first one is the main rotor head of a Bell 222, the second one is the tail rotor of a Robinson R44.

Main rotor of Bell 222. Source: Wikimedia Commons

Tail rotor of Robinson R44. Source: Wikimedia Commons
For the Bell 222, the red line of the pitch hinge is perpendicular to the blue line of the flapping hinge (also called teetering hinge in this particular design). For the R44, the red line and the blue one are not perpendicular but intersect at some 45°. Hopefully this difference is visibile despite the different perspective of the pictures. This not-perpendicular intersection like in the R44 is the delta-3 angle.
Now, when a blade of the B222 flaps upward... well it just flaps upward. When the blade of the R44 flaps upward (actually "outward" is maybe a more correct term for a tail rotor but for ease of comparison I stick with upward) it flaps upwards... and it reduces it's pitch, exactly because these two axis are not perpendicular due to delta-3.
That's not very easy to represent but it could become clearer looking at an extreme case: starting with the B222 configuration and its 90° shifted blue and red line, let's reduce this angle (i.e. increase delta-3); we get to the R44 configuration with its 45° between blue and red line; now let's reduce this angle again (i.e. further increase delta-3) till we get to the extreme case where blue and red line  overlap (i.e. delta-3=90°): now flap and pitch have become the same thing, they both lie on the same axis, they are coincident, 1° of flap coincides to 1° of pitch. To sum up:

blue and red lines perpendicular (B222) $\Leftrightarrow$ $\delta_3=0°$ $\Rightarrow$ flap and pitch fully decoupled
blue and red lines coincident $\Leftrightarrow$ $\delta_3=90°$ $\Rightarrow$ flap and pitch fully one-to-one coupled
$\delta_3$ between 0 and 90° (R44) $\Rightarrow$ flap and pitch partially coupled.

(This latter partial coupling is mathematically translated as $\theta_{\delta_3}=\beta tan \delta_3$, where $\theta_{\delta_3}$ is the change in pitch due to the flapping $\beta$. Maybe if you have some Lego technic laying around you could try it out and verify it live).
What's the benefits of that? As said, when the blade flaps upward (outward) the delta-3 makes its pitch reduces which, in turn, reduces the aerodynamic thrust generated by the blade which, in turn, reduces its flapping. The opposite is true when the blade flaps downward (inward) i.e. the delta-3 makes the pitch increases, increasing its thrust and therefore its flapping:

blade flaps $\Rightarrow$ due to $\delta_3$ pitch reduces $\Rightarrow$ lift reduces $\Rightarrow$ flap reduces

So delta-3 is a simple cinematism used to limit the amount of flapping of the blades of the rotor.
This has a twofold outcome:

clearance between tail rotor and tailboom is reduced giving a shorter and lighter shaft;
flapping produces also lead-leg movement via the Coriolis force; if flap is reduced also lead-leg movement is reduced and it can be reduced to the point that the lead-leg hinge can be disposed of, as in the R44.

Free weight saving is always good in the aerospace world.

Bonus material
Delta-3 is used exactly for the same reason also on the main rotor, anyway in a milder way since flapping is the physical effect which permits the control of the helicopter, so a compromise between shorter/lighter mast and controllability is needed here.
Since on the red line only 2 blades can lie, for rotors with 3 or more blades the delta-3 effect is obtained with a different cinematism: if someone is interested in it, I could expand this answer.

I wanted to add that these “dynamic stabilization” examples occur all throughout aerodynamics, even the way an arrow flies.  Perturbations happen throughout each rotation of the rotor.  I can have a more rigid mast that imposes structural force on the rotor to counter the perturbation.  Or I can have a lighter mast with less vibration transferred to the aircraft if I design the hub in such a way that the “correcting” force is NOT applied to the blades by the mast, but rather by aerodynamic forces acting on the blade.  I hope this adds the “why?” Context to sophit’s “how” answer.

@sophit, isn't the equation, $\theta_{\delta_3}=\beta tan \delta_3$, only valid when the delta-3 angle for pitch flap coupling is implemented by the control system geometry? I believe relationship you describe above (in words before giving the equation) is true when the delta-3 angle for pitch flap coupling is implemented by the flap hinge geometry. Note, in your example, when $\delta_3=90$, $tan \delta_3=\infty$, not 1. (Ref: Wayne Johnson, Helicopter Theory, pg 239)

Also note that the formula $\theta_{\delta_3}=\beta tan \delta_3$ is approximate because it assumes $\theta_{\delta_3}$ and $\beta$ are small angles.

@eball: yes correct, thanks for spotting it. If think I'll remove the equation, nobody is anyway going to use it :)

@eball: have you spot any other error or needed improvement?

@sophit, nothing else pops out at me. Nice work!

@eball: ok, thank you very much

Thanks for the response! Very helpful!

Your explanation does not work for the Bell 429 (and others).  They have the delta 3 hinges the other way around.  As the blade flaps, the feather angle also increases which would seem to amplify any vibratory mode.

@GeorgeWilliams: note that on the B429 the pitch link is by the trailing edge while on the R44 is on the leading edge and all the reasoning is therefore the other way around. Please do not downvote randomly if you don't understand something, it's very unfair...

Unfortunately the other explanations are wrong because they do not cater for for the negative delta 3 angles found on Bell 407, AW139 and Bell 429.  Here's a different perspective.
Hinges on rotor blades do not necessarily have to be perpendicular to the blade axis and the behaviour of the rotor can be tuned by angling hinges or moving control rods to provide coupling between the drag, feathering and flapping of blades.

Juan De La Cierva experimented with various axes during development of the autogyro in the 1930s and produced a naming convention to describe the hinges. The delta 3 hinge is a hinge where flapping and feathering motions are coupled with the hinge lying in the plane of rotation (delta refers to the feather/flap cross-couple and 3 refers to the plane of rotation).

Without a delta 3 hinge a degree of cross coupling is still likely on the rotor blades as the pitch rods remain fixed while the rotor blade flaps, inducing pitching or dragging motions. These motions can be undamped and oscillatory leading severe vibration. Cierva found that by change the angle of the hinge of the blade he could reduce the maximum flapping angle of his unpowered rotor which has a lot in common with the tail rotors of today.
The delta 3 hinge can be either at a positive angle (increased flapping results in decreased feather angle) or a negative angle (increased flapping results in increased feather angle).  A positive delta 3 angle is shown below. Note the pitch change rod is in front of the blade for this positive delta 3 unlike the Bell 429 shown at the start where the pitch change rod is behind the blade for a negative delta 3 angle.

Each option provides several advantages for the designer, particularly with reference to the tail rotor:
a. Simpler layout of control rods in tail rotors with greater than 2 blades.
b. Reduced vibration as the point of maximum flapping and maximum feathering can be phase shifted away from each other.
c. Reduced flapping angles due to phase shifting the point of maximum flapping from maximum feathering with either positive or negative delta 3 hinges.
d. Damping of tail boom oscillations dependent on the structure of the tail boom
Of course, as with everything on helicopters it is not a free ride, so the choice of hinge could also increase vibration. The choice of hinge is also heavily dependent on whether the blade has a hinge offset. A negative delta 3 with a hinge offset is a recipe for high vibration levels according to the research.

The delta 3 hinge can be created by introducing a change in the hinge itself or by locating the pitch change rod such that the motion of the blade as it flaps introduces the appropriate motion. Typically tail rotor pitch control rods are located in front of the blade for positive delta 3 effects or aft of the blade for negative delta 3 effects. The lead angle of positive delta 3 inputs tends to be larger than the lag angle of negative delta inputs due to the potential for further vibration effects at large negative delta 3 angles.

Thank you for the informative response!


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Does one-engine cruise consume less fuel than two-engine cruise?
Scenario 1. A two-engine airliner experiences rapid depressurization and makes an emergency descent to 10,000 ft, and diverts to the nearest airport.
Scenario 2. The same two-engine airliner experiences rapid depressurization after it has lost one of its two engines and makes an emergency descent to 10,000 ft, and diverts to the same nearest airport.
In which scenario between the two does the airliner consume a greater amount of fuel, and why?

(1) I'm not sure it's reasonable to refer to "cruise" at 10,000 ft for an airliner. (2) Are we to assume identical airspeed in scenarios one and two? (3) With one engine inoperative of two (for any reason), how does the aircraft maintain directional control? What does that do to the amount of drag the engine must overcome?

All the other conditions not mentioned above were assumed to be the same. Therefore, the speed is the same, and no additional drag is being made to the one-engine aircraft due to the one-engine condition.


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How high are you when you are three miles away from the threshold of the landing RWY and get 3 white and 1 red on PAPI?
Let's say you were shooting a visual approach and you were precisely on a three mile final. You gave a glance at the PAPI, you find it giving three white and one red. How high you are from the 3 degree glide path at the moment?
Anybody can do math for me?

Depends on the angle to which the PAPI is aligned.

According to AIM 2-1-4, three white one red would equal 3.2 degrees above the horizontal. Doing some math, and assuming you are 3 NM from the TDZ (ie the PAPI) and ignoring slant range error, 3 NM would put you 18,228 ft from the threshold. Assuming you were on the 3 degree PAPI glideslope, you would then be 955.3 ft above TDZE. If .2 degrees high, or 3 white one red, you would be at 1019.1 ft above TDZE, or about 64 ft above the correct glideslope.
Math if you care: [tan(3.2)*18,228]-[tan(3)*18,228].

Bravo! Thanks :)

That depends on the angle of the PAPI though. Not all runways have the same approach angle.

@J.Hougaard while this is the case, I was working off the information available in AIM 2-1-4, which states the PAPI glidepath is 3.00 degrees.


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Why is a clock required to be mounted on the instrument panel for IFR flights?
A clock is required for IFR flights in the US but any clock doesn't do; the clock should be the one mounted on the instrument panel. What's the idea behind this requirement? Is it because random clocks the pilots might carry with them for their flights cannot be trusted?

The clock needs to be positioned such that you can see it easily as part of your instrument scan, and the sweep second hand needs to be there to make it easy to time intervals that are not whole minutes.
The regulation has been there for a long time, so the requirement should be considered in the light of how things used to be as well as what they are now.
A very practical example from 1969 follows. The regulation predates that by many years, I am sure, but the 1969 environment shows the need.
You're in a light single engine airplane (think Cessna 150 and later a Cessna 172). You're working on your instrument rating in actual conditions in the Pacific Northwest in a non-radar environment. You're in moderate turbulence and having to keep on eye on the icing. And, though it seems ridiculous now, we didn't use headsets but instead picked up a mic for each transmission, of which there were many because in the non-radar environment there were lots of reports.
You're inbound to the VOR on the airport, after which you'll proceed outbound to the NDB that is the final approach fix. Once at the NDB, you will fly 30 seconds farther outbound on the Rwy 16 ILS, which by the way since you have no HSI you're having to navigate by reverse sensing on the old VOR/ILS CDI with its swinging left/right needle. At the 30 second point, you're to turn right to the procedure turn outbound course and fly for 45 seconds (but maybe if that wind is from the east you should go for 60 seconds - better watch that CDI needle to see how fast you get full deflection).
Oh, damn, the instructor just covered up the directional gyro to simulate its failure. Now your only heading reference is the wet compass, which is bouncing around in the turbulence, and, besides, you can't remember whether it's going to precede or lag (and by how much) in the turn you have to make to reverse course for the inbound leg of the procedure turn. Ah, but wait, all you have have to do is fly a standard-rate turn for 60 seconds and you'll be in good shape.
So, thus far, we've had three separate needs to time things to seconds in a situation where we have our hands full - left hand on the yoke, right hand for throttle, carb heat, microphone.
Given all that, do you really want to have to keep pulling back the sleeve on your left arm to monitor a relatively small clock face? Much better to have a larger clock face right in front of you on the instrument panel.
Do we really need such a clock now? Perhaps not, but it doesn't hurt, and regulations are notoriously resistant to change.
And does anybody actually fly procedure turns anymore?

Upon reading this I have decided not to take flying lessons after all.

@A.I.Breveleri Take heart and go ahead, today's environment is far better, easier, safer. Electronic gyros which don't fail like the old spinning ones, autopilots common in training aircraft. HSIs (horizontal situation indicator) or glass cockpit displays that do away with having to think of reverse sensing. And when I tried to look up the outbound course of the procedure turn for the KEUG ILS Rwy 16, I found out they don't even show a procedure turn anymore. No longer necessary in the radar environment. Really, from this old fart's standpoint, they've taken all the fun out of it.

@A.I.Breveleri You have no idea how many ADF's go inop on the day of an instrument check ride... This all sounds complicated and your instructor may have you do it once during training, but I've yet to year of an examiner pulling something so complicated. It is fun stuff to try when you have the instructor next to you, in real life you would ask for the nearest VFR airport and divert. Honestly if you took off in a 150/172 in icing/moderate turbulence I'd have to question your instructor's grasp on life.

When I was young, we had to do all @Terry describes, plus wiggle the mic plug to get the audio to come out right.  We also had to be careful where the charts were left, because in the rain everything leaked big time. At least back then much of the airspace I flew IFR in was uncontrolled, so we could just kick the tire, light the fire, and air file while tooling around in uncontrolled airspace.  The payphone at the airport, and the 300 yard dash to the airplane in the rain after a FSS clearance, was a real pain when operating in controlled airspace. There were few RCOs, and no cellphones.

@mongo And, as you allude to in your dash from the payphone to the airplane, you had to watch the clock because your clearance included a "void if not off by" time which was not that far in the future. A time that was necessary because they had to block off the controlled airspace you would be headed into until they either heard from you or the time expired.

So if we don't need a clock, under 91.205 now, where will the requirement be for a pilot to carry one?  From a regulatory standpoint, it is easier to have one in the aircraft, and to have it part of the MEL or some other requirement.

All these require a timer, not a clock.  Having spent many years with automotive clocks (which only got accurate when they got digital), all I can think of is "how do they absolutely guarantee the clock is  accurate, because a clock that is wrong is far more dangerous than no clock at all."  Today of course GPS answers that question, you ask the satellites.  Until they turn it off due to terrorist threat, and then you cannot fly at all.

@Harper You are correct that the aforementioned uses of the clock are all as a timer. However, there are instances where the time of day needs to be referenced. For example, the final part of holding instructions from ATC typically will be something like "expect further clearance at xx:xx" or "expect approach clearance at xx:xx." The time given will be the UTC time in 24 hour format, except that you may be given just "xx" which is to be interpreted as that number of minutes past the current hour.

Regs are hard to change because of familiarity.  When you get used to a clock being in a certain place, its utterly impossible to train yourself out of looking there.   I haven't worn a wristwatch for 25 years and recently caught myself looking at my wrist for the time.   If you doubt the power of habit, try moving, removing, or covering a clock that you use frequently at home or in the car.

Just happened to watch an episode of Mayday last night where the pilot flew into a mountain because he didn't check the stopwatch. Why he continued a circling approach in clouds is anybody's guess

I was looking around for some info on this instrument panel mounted 1960's era stopwatch clock.  I was confused because it had its own built in heater AND was vacuum sealed.  This explanation makes a lot of sense on why you need such a well built piece of equipment.

We actually had a guy get busted for this.  No approved clock installed on the aircraft.
After that happened, we took out all the broken mechanical clocks on our aircraft, and installed digital clocks, with batteries and a 12V feed, and a 12V panel lighting wire.
Legally, you can have all the stopwatches and wristwatches you want, but for instrument flight, there must be a clock installed.  I have been told by an FAA Avionics Inspector that a GPS or other piece of avionics with a clock satisfies the requirement.  Back when we had LORAN-C, one of the units had a timer in it, and we did not have a clock on that aircraft. I cannot remember an aircraft GPS which does not have a clock feature.

I chuckle at a GPS without a clock, given my engineering background.  GPS figures out where you are by having clocks accurate to nanoseconds.  The idea of using these mighty impressive clocks in this way, then not presenting a clock to the user, is terribly amusing.

@CortAmmon Yeah, you know you have some seriously precise time measurements involved in your system when you end up having to take general relativity into account.

Agreed, the voting of multiple atomic clocks gives some pretty accurate time for determining MAP, or reporting an intersection. The real point of 91.205 is that it establishes the equipment requirements, not what the pilot must carry on board to supplement the equipment.

@reirab While you do have to take relativity into account, that article is false. GPS measures the difference between pulses from satellites, and relativity affects all the satellites similarily. So without relativity corrections, the pulses would come slightly less often, and the satellite wouldn't be exactly at its calculated position. However, since all signals come in at (almost) the same delay, the difference is unchanged. So instead of the error being of the scale of light speed times relativity time shift, it is on the scale of satellite orbit velocity times relativity time shift.

(The pulses would come slightly more often, but I was too late to correct it.)

Among all clocks and watches it should be many models that are just unsuitable (cheap/unreliable, strange design, etc). There is a certain risk that clearly unsuitable model would formally match the requirements, or may appear it is doing. For instance, "digital presentation" - binary ok?
If the watch is a part of the plane it probably has passed the certification so should be bearable.

I would like to point out that the FAA's answer says that the clock can be an "installed appliance with a permanent clock display that meets the requirements of§ 91.205(d)(6) that displays "hours, minutes, and seconds with a sweep-second pointer or digital presentation," is adequate for the purposes of this regulation." Please note that it points out that the clock display is permanent.  I interpret this as the GPS must have a clock visible on its screen no matter what page you are on.  In other words, if you have to change the GPS page to see the clock, it is not legal.  Some GPSs and PFDs display the clock constantly, no matter what page you're on.  These are legal.

Here’s the FAA’s official answer about clocks...
https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/Interpretations/data/interps/2016/Nkugba%20-%20%282016%29%20Legal%20Interpretation.pdf
Yes, your GPS clock is okay. If you have a garmin transponder like the Gtx 327, 330, etc. they have a great timer function...

Welcome to aviation.SE! We prefer answers to be 'self contained' rather than simply link to another source. If the link becomes invalid for some reason then the answer isn't useful any more. I suggest you add the most important point(s) from the FAA source in your answer. If you're new to the site, the [tour] may be helpful.

If there a way to directly upload the documents to the site? It succinctly answers the question bring asked, and is an official FAA ruling. That takes away the uncertainty of someone saying I read it on the internet...

No, the site doesn't support uploads (apart from images). The usual practice is to quote the most relevant part and link to the source. See this answer, for example.


text:
When is the use of reverse thrust recommended in airline operations?
I know the answer largely depends on each airline's FOM but I still wonder what the FOMs generally recommend with regard to the use of reverse thrust after landing. For example, I guess its use would be generally recommended for the accelerate-stop maneuver and also for landing on short runways.
So once again, what're their general recommendations on the use of reverse thrust after landing, if any?

Not really a duplicate, the selected answers says it used on the ground, no other details.

The main use of Reverse on landing for big-fan engines is to kill the residual forward-thrust rather than to actually supply braking airflow. This offloads the (wheel-)brakes.
If the runway is short, then the wheel-brakes will need assistance to get the aircraft stopped in time, and then you'd use more Reverse. Some aircraft have an Intermediate Reverse click-stop, which allows you to use a standardised mid-level of Reverse; and then there's Full Reverse, but that gets noisy, which some airports don't like (especially at night).
The level of Reverse used is the P1's decision, while complying with aircraft performance on that runway, the airport's noise policy and the airline's balance between engine wear and brakes wear.

The first paragraph is incorrect. Reverse thrust provides quite a bit of "braking airflow".


text:
Our pilot lost the logbook
Our company pilot lost the aircraft logbook for about 15 years worth of flights.  Boxes of stuff.  Who knows how he lost it.  We now want to sell the aircraft - can FAA reconstruct the logbooks?  If costs are involved can we get the pilot to pay for it?

The FAA doesn't get copies of your logbook periodically, so they can only vouch for registration data or if a major repair/STC were performed (337). The linked question by fooot is good, basically you need to do a very thorough annual and have an A&P verify that all the AD's are complied with (which may require tear-downs). This can be very expensive. As for getting the pilot to pay for it, that is something your lawyer is going to have to answer.

Plan on getting about 50% the blue book value of the plane if you can even find a buyer.  You can try to make the pilot pay for it but you'll spend a lot of money on that with a pretty good chance that the pilot will never be able to pay you back even if you are successful in securing a judgement. Find those books.  What kind of plane is it?

We now want to sell the aircraft - can FAA reconstruct the logbooks?

As @fooot mentions in the comments you can find most of the details on this question here. There is a brief AOPA article here.

If costs are involved can we get the pilot to pay for it?

For this you need to consult a lawyer (I would try and get one that specializes in aviation related cases). Depending on how his contract (if he has one) with your company is arranged you may have some weight here. There is a nice document covering a lot of cases in this space that you can find here. See section VI, but you may be covered for this under your insurance,

VI. LOST, STOLEN OR DESTROYED LOGBOOKS
  MAY BE COVERD UNDER THE AIRCRAFT'S
  INSURANCE POLICY.
Lost or destroyed logbooks may be covered under the aircraft’s
  insurance policy. However, whether or not coverage exists will depend
  on the language of the policy and, if the logbooks are not
  specifically covered under the policy, an insurer can deny coverage
  and a court may have to decide whether coverage exists.

I would seriously take time to look for them prior to doing anything as Im sure you already have. You can take a look at this thread for some info on rebuilding logs.
It is also worth reaching out the aviation shop that you use to maintain the plane. Many shops may have work records on file that can help you rebuild your records.


text:
Is there specific verbiage required to close out an engine logbook and start a new one?
The plane's engine logbook is now full, victim of decades of individual printed stickers, each one occupying a full page. As a result, we need to get an additional logbook.
Is there specific phrasing the FAA likes to see for closing out an old engine/airframe/propeller logbook and starting a new one?


text:
What are the pros and cons of putting a propeller immediately before a slipstream pylon vs. immediately after
In the following situation with a slipstream pylon for a self-launching glider, what are the tradeoffs in sticking the propeller before vs. after the pylon?

The wind turbine industry has the same conceptual problem, and their consensus is that the turbine is better with the blades in front of the support tower. However, their support tower is circular and so induces unacceptable turbulence and pressure pulses in the turbine blades. Their system is also designed to operate for decades.
Contrast this to the case in question, where the pylon is slipstreamed and so has significantly lower drag and wake turbulence. My hunch, then is that it seems that behind the pylon is better because the airspeed across the pylon is much lower.
However, I am loathe to reject the wind turbine industry findings with some hand waviness about "slipstreamed" profile.

If it's for something like an airplane or powered glider, for best thrust efficiency and noise level, you want the prop on the front. If behind, the turbulence from the pylon causes both efficiency loss and a loud buzz as the blades pass through the pylon's wake. This is a bigger deal than the effect of the prop's wake hitting the pylon when mounted forward.  The characteristic buzz sound that the Lake Buccaneer makes is from having the prop behind the pylon.
For an engine on skinny pylon with little frontal area, the difference between pusher and tractor is not that much, so noise effects are probably a bigger issue.  The efficiency difference grows when the body in front of or behind the prop gets large. From an article by designer Peter Garrison in FLYING:

Now, how to compare this with the efficiency efficiency of a pusher propeller? For this I'm obliged to turn to books, since it's not possible to do a rule-of-thumb calculation from basic physical principles, as it was for the tractor. In Roskam and Lan, Airplane Aerodynamics and Performance, there is a chart showing the effect of what you might call the occlusion ratio -- the ratio of fuselage diameter to propeller diameter -- on the efficiencies of tractor and pusher propellers. The efficiency of the pusher prop is lower than that of the tractor, but negligibly so, until the fuselage diameter reaches half the prop diameter, at which point the two curves begin to diverge. When the fuselage diameter is 60 percent of the prop diameter the pusher has dropped behind by about 3 percent; by the time the fuselage diameter is 70 percent of the prop diameter, the decrement is 8 percent. An equation is provided (it is also found in Dan Raymer's Airplane Design: A Conceptual Approach) that yields roughly the same result.

The Volmer Amphibian is a good illustration of this.  It had the option of doing either; you could design the mount to point the engine forward or backward.  Part of the attraction of the tractor option was it didn't limit the engine choices (you need an engine with thrust bearings for pusher installation if you want to install it that way, as well as a prop designed for pushers).
Having the prop forward is widely seen as more efficient, with better thrust for the same horsepower and a simpler installation.  I would say most Volmers were built as pushers however, mostly due to discomfort with having a propeller blade tip passing a foot and a half behind the pilot's head (I'd not be too happy having to put the thing into trees with that head chopper right behind my head, and if I was building one, there is no way I'd have the prop on the front).
The consensus however, seems to be that the tractor arrangement is superior performance wise, while the pusher is safer.
In the case of an electric motor glider (which I assume is what you are contemplating) there is another factor, which is the desirability of an aft folding propeller if the mount is fixed.
Recognizing that the efficiency difference may not be enough to worry about although the noise effects could be significant, if the pylon retracts, I'd put the prop on front. If the pylon is fixed and the prop feathers, I'd also put it on the front.  If the pylon is fixed and the prop folds, then it goes on the back.

Good stuff! What kind of quantitative difference is there for the fore vs aft mounting?

Wouldn't the prop slipstream cause more drag on the pylon in the tractor arrangement? The noise argument is convincing (and easy to check) but the performance claims need more than just some handwaving.

@PeterKämpf I've been reading Peter Garrison's columns since the 70s and found the column where he talks about it.  Made some edits for better clarity and less hand waving.

The airflow downwind of the propeller will be moving significantly faster than upwind, since the incoming air is drawn over a wider angle than the outgoing air, which is more or less a cylinder.  Also bear in mind that the outgoing airflow will be rotating in a helix and so will impart a sideways force to the pylon.  If the pylon isn’t circular in cross-section then it should be designed to take account of the airflow direction (which may be best established experimentally.  Don’t be surprised if the airflow is at 45 degrees to the direction of travel.

That's a really good point about the airfoil orientation.

If you can find a video of the ‘flying cars’ episode of Scrapheap Challenge (UK, c.2001) you’ll see that one team came totally unstuck by not taking this into account :-)


text:
For a same propeller solidity, what are the tradeoffs between blade activity factor and blade number?
In order to absorb more power for a given prop diameter, we can design the propeller with a higher activity factor-- basically what amounts to wider blades-- or we can also design it with more blades. Both increase the solidity, and thus the ability to produce more thrust, but what drives optimal design? Longer chords mean more drag on an individual blade, but more blades mean more disruption of the airstream. Why and when choose one over the other?
Low blade count, low activity factor:

Low blade count, high activity factor:

High blade count, low activity factor:

High blade count, high activity factor:

One way look at it is your engine is power and prop is load.  The amount of thrust you get will depend on the efficiency of the propeller x engine power output.
So, if one is going for the best fuel economy, the two blade is most efficient, but if you want the more thrust from a larger engine, you either increase the number of blades or increase the chord of the blades.
Both approaches reduce efficiency but increase thrust output, resulting in increased performance.
More high aspect blades, as in a helicopter, will be more efficient at lower airspeeds, but will suffer structural issues (bending) as forward airspeed increases.
Fewer low aspect blades offer a much higher forward speed range but will create a lot more blade interference turbulence at lower airspeeds.  These are commonly seen on turboprop freighters such as the C-130.
It is extremely important to evaluate the design speed envelope of the aircraft when choosing, as forward airspeed reduces interference turbulence.
I took the liberty of adding the A6 Intruder jet aircraft to your list, and found the expected improvement in higher airspeed performance, but a take off run almost 5 times that of the A2D-1 Skyshark.
Enough said there.  Contra rotating coaxial props, and keeping prop speeds below supersonic, also help improve efficiency.

Any chance you could update this with some more detailed examples of optimization? I don't quite follow why high activity factors will improved forward speed range.  P.S. I don't understand the reference to the A6.

@Kenn Sebesta the jet engine, with its rows of blades, is an extrapolation of high blades, high activity.  It is better to have more, higher AR blades, but lower AR are stronger.  Forward speed reduces blade/blade interference.

High activity, high blade count enables more horsepower (more fuel/unit time) to make more thrust, increasing forward speed.  Comparing prop to jet was irresistible.  Just swinging the 2 blade faster and faster is constrained by the sound barrier.

so, you have a choice:  more thin blades or increasing chord.  More thin blades are better, but not nearly as strong.

(Notice the biplane also has 2 wings.  It is much stronger per unit wing area, able to handle higher +/- G loads).


text:
Why do few small planes have reflexed flaps?
Reflex flaps capability is very common in flapped gliders, but outside of gliders I am only aware of the Maule which has this feature. https://aviation.stackexchange.com/a/37753/20394 shows the advantage gliders gain from reflex position, so presumably this would hold for more aircraft than just gliders.

I can see how with certain types of flaps, such as fowlers, the mechanism would be impossibly complex. But for other types with a simple pivot this must be more attainable.

This is a good question, although I'll admit I'd never heard of a reflexed flap mechanism prior to reading your question here. :)

I'd guess that it's because gliders are optimised for low speed in rising air and their aerofoils have lots of camber. Reflexed flaps allow them to reduce the camber for high speed flight, but the resultant aerofoil isn't as good as a proper low-camber, high speed aerofoil.
RC power models generally have plenty of power to spare and either don't care about drag or it only matters at high speeds. Their aerofoils are generally low (or zero) camber already so they don't need reflex flaps to achieve it.

Reflex reduces lift, so whether there is camber or not shouldn't eliminate the effect from reflexed flaps. Considering the extents people go to to pick up a knot or two of airspeed, it seems reflex might be a solution. Perhaps it is only worth the cost when you have a plane designed to spend significant periods at both slow and fast speeds? Most small planes only fly slowly to land or right after wheels up.

Reducing lift isn't the same as reducing drag. If you start from an aerofoil that's optimised for high speed, adding reflex would just add drag. Reflex is a compromise to make a low speed aerofoil act a bit more like a high-speed aerofoil, not a magic bullet that makes everything faster. Gliders are designed for low speed and need it, power planes are designed for cruise already, so they just use flaps for low speed.

"...power planes are designed for cruise already," Is this generally true? On one hand, it makes sense that a cruise plane would be optimized for cruise, but on the other hand there are all kinds of design features which detract from cruise. For instance landing gear, which imposes a huge weight and/or drag penalty yet is only useful for the 3 minutes at the beginning/end of a 5 hour flight. So my earnest question is "are power planes' airfoils able to be optimized purely for cruise, without consideration of slow-speed lift?"


text:
Understanding "non-WAAS G1000" in a 2006 Turbo 182
All,
I am trying to get my head around something my local avionics shop is telling me about a 2006 T182 that has a GTX345R fitted. Surely, the GTX345R adds WAAS capability but he referred to this configuration as a "non-WAAS G1000"
I feel like you'd need to be Stephen Hawking to understand this stuff!
Can anyone shed light on the way in which the addition of a GTX345R (replacing GTX-33) means it is not WAAS???
Thanks in advance,
Michael.

The GTR345R is a transponder that can be purchased with a built-in WAAS GPS (link)—which this one apparently has. So it provides the WAAS GPS positioning required for ADSB. The GPS in the transponder does not provide a GPS source to the G1000.
From what the shop said, it looks like the G1000 is an older version that is not WAAS capable. That’s probably why they chose to install the transponder with built-in WAAS since it was much cheaper than upgrading the G1000.

"The GPS in the transponder does not provide a GPS source to the G1000."
That was the info I was missing - thank you for the quick and easily comprehensible response!


text:
How do I get a copy of a Pilot Operating Handbook?
I need the POH for a Cassutt Plus or any variation for a University Project but I can't seem to find anything on the plane.
Any other information (flight capabilities etc) would be helpful - with references if possible!
Thanks

Hi Chloe, and welcome to Aviation.SE! Please take the tour to learn how this site works.
I'm afraid resource location questions are considered off-topic here so this may get closed either for that or because it is excessively broad. If you could narrow it down to the specific data you need, it would be better. Good luck with your project, and I hope you stick around.

Doubt you'll find one. Homebuilt plane like that would not have had a POH written like a factory certified plane would have.    A couple of the Cassutt planes are mentioned in this book  https://books.google.com/books?id=3_63vTcxl0IC&pg=PA162&lpg=PA162&dq=Cassutt+Plus&source=bl&ots=GWeXoKkG20&sig=ACfU3U25FyXEwe0mSpfXbd41lYEK5TPJJA&hl=en&sa=X&ved=2ahUKEwi0u_3jg4DlAhXPJt8KHS6-ChYQ6AEwB3oECAkQAQ#v=onepage&q=Cassutt%20Plus&f=false with plans marketed by National Aeronautics Company, which doesn't seem to be around  under that name anymore.

Generally you won't find published POH documents for plans built homebuilts, as each aircraft is unique, the individual builder being the "manufacturer".  Possibly, a builder has made his own POH. Best bet is to write to the guy currently marketing the plans and selling parts, Creighton King.

thanks for the help


text:
How many US airports have 4 or more parallel runways?
Which airports in the US have four or more parallel runways?
How many are planning additions in the next 5 years?
A few years back, 10 years, Charlotte opened their 3rd parallel runway and it was said to be only one in seven in the country. Just wondered if there is an updated number for 4+ runways. I have searched and some sites have great information but I am not sure it is up to date. Not trying to offput just looking for information that might not be posted to the public.

Hi and welcome to [Aviation.se]! Please take the [tour] and read through the [help], especially on what makes a good question. Knowing this info will help us help you better.

@WilNeumann: I think it will help if you narrow down your definition of "parallel runway". If you look at Bianfable's answer, for example, it includes KDFW (Dallas/Fort Worth International Airport) with runways 13L/31R and 17L/35R which in my opinion are not really "parallel" and runways 13L/31R and 13R/31L which while meeting the mathematical definition of "parallel", are actually on opposite ends of the airport and so don't meet the colloquial interpretation of "parallel" which implies proximity.

@JörgWMittag Runways 13L/31R and 17L/35R at KDFW are not parallel and have never been counted as parallel runways. I simply listed all runways the airport has (now updated for more clarity).

That would seem surprising for CLT to be only one of 7 with 3 or more parallels. Even BNA has 3 parallels and has for as long as I can remember (certainly much farther back than 10 years.) ATL and ORD have 5.

@JörgWMittag At least in the U.S., 'parallel runways' doesn't not imply proximity, other than that they are at the same airport. It just means the number of runways at that airport that are parallel to each other and, thus, can be used for simultaneous flight operations. For example, ATL has 5 parallel runways, so it can do 3 arrivals and 2 departures (or 2 arrivals and 3 departures) at the same time without interference. The runways are spread out enough laterally that they don't interfere with each other's operations. Within a pair, one is used for takeoff and the other for landing.

Based on my current navigation database (AIRAC 1909, valid from 2019-08-15), I found 7 US airports with 4 (or more) parallel runways:

KATL (Hartsfield–Jackson Atlanta International Airport):
5 parallel runways: 08L/26R, 08R/26L, 09L/27R, 09R/27L, 10/28
KDEN (Denver International Airport):
4 parallel runways: 16L/34R, 16R/34L, 17L/35R, 17R/35L
and 2 more parallel runways: 07/25, 08/26
KDFW (Dallas/Fort Worth International Airport):
5 parallel runways: 17L/35R, 17C/35C, 17R/35L, 18L/36R, 18R/36L
and 2 more parallel runways: 13L/31R, 13R/31L
KDTW (Detroit Metropolitan Airport):
4 parallel runways: 03L/21R, 03R/21L, 04L/22R, 04R/22L
and 2 more parallel runways: 09L/27R, 09R/27L
KLAX (Los Angeles International Airport):
4 parallel runways: 06L/24R, 06R/24L, 07L/25R, 07R/25L
KMCO (Orlando International Airport):
4 parallel runways: 17L/35R, 17R/35L, 18L/36R, 18R/36L
KORD (Chicago O'Hare International Airport):
5 parallel runways: 09L/27R, 09R/27L, 10L/28R, 10C/28C, 10R/28L
and 2 more parallel runways: 04L/22R, 04R/22L

I do not know how many are planning additions, but I linked the Wikipedia article for each of the airports, maybe that will help you find more information on that.
Trivia: There are only 3 airports outside the US with 4 parallel runways: LFPG (Paris Charles de Gaulle Airport), LFTM (Istanbul Airport) and ZSPD (Shanghai Pudong International Airport).

The Wikipedia article for O'Hore says they are currently working on adding a sixth parallel runway, bringing the total to 6+2...

Fairbanks International Airport (PAFA) lists 4 parallel runways. 2L/20R, 2R/20L, 2W/20W, and 2/20.  The catch is 2W/20W is a water runway for float planes and 2/20 is a dirt/gravel runway used for ski planes.

@Gerry nice catch! My database does not include the water runway, that's why it did not show up.

ATL is indeed the world's biggest (busiest?  something) airport, so it makes sense it's in the list, I guess.

@Fattie It is indeed, by passenger numbers. ATL had 107 milliion passengers in 2018. Interestingly, Europe's busiest airport (London Heathrow) with 80 million passengers only has 2 runways!

thanks for that!  @Bianfable  ATL is surely the best of the very large airports, IMO

@Bianfable US airports have abnormally low average seats per aircraft due to all the regional airlines, so they need more runways to move the same number of people.